The present invention relates to a touch panel device for detecting the touch of a finger or an object on the touch panel device, and more particularly relates to a touch panel device using IDTs, for detecting a position touched by the finger or object by detecting a cutoff of surface acoustic waves.
With the spread of computer systems, mainly personal computers, there has been used a device for inputting new information or giving various instructions to a computer system by pointing at a position on a display screen of a display device on which information is displayed by the computer system, with a finger or an object. In order to perform an input operation with respect to the information displayed on the display screen of the display device of a personal computer or the like by a touching method, it is necessary to detect a touched position (indicated position) on the display screen with high accuracy.
Well known examples of touch panel device for detecting a position touched by a finger or an object are a device using a resistance film, and a device using ultrasonic waves. In the former device using a resistance film, a change in the resistance of the resistance film caused by the touch of the finger or object on the resistance film is detected. This device has the advantage of low consumption of power, but has the problems in the aspects of the response time, detection performance and durability.
By contrast, in the device using ultrasonic waves, a position touched by the finger or object is detected by propagating a surface acoustic wave (SAW) on a non-piezoelectric substrate, for example, and detecting attenuation of the surface acoustic wave caused by the touch of the finger or object on the non-piezoelectric substrate. In conventional touch panel devices of the ultrasonic wave type, however, since transducers for generating the surface acoustic waves and detecting the same are formed by ceramic transducers, this type of touch panel devices have problems, such as difficulty in reducing the thickness and size, higher costs of the parts and difficult mounting, in comparison with the touch panel devices of other types.
Therefore, there has been proposed a touch panel device using IDTs (Inter Digital Transducers comb-like electrodes) which can be formed collectively using a photolithography technique as transducers. This touch panel device uses elements, each constructed by an IDT and a piezoelectric thin film, as an excitation element for exciting a surface acoustic wave and a receiving element for receiving a propagated surface acoustic wave.
FIG. 1 is an illustration showing the structure of such a conventional touch panel device using IDTs. In FIG. 1, numeral 1 is a rectangular non-piezoelectric substrate made of a glass material, and a plurality of excitation elements 2, each constructed by an input IDT and a piezoelectric thin film, for exciting surface acoustic waves are arranged into a line on one end in each of the X-direction and Y-direction of the non-piezoelectric substrate 1 so that the excitation elements 2 correspond to a plurality of tracks, respectively. Moreover, a plurality of receiving elements 3, each constructed by an output IDT and a piezoelectric thin film, for receiving the surface acoustic waves are arranged into a line on the other end in each of the X-direction and Y-direction of the non-piezoelectric substrate 1 so that the receiving elements 3 face the excitation elements 2.
In the touch panel device shown in FIG. 1, an electric signal is input to each excitation element 2 to excite the surface acoustic waves and propagate them on the non-piezoelectric substrate 1, and the propagated surface acoustic waves are received by the receiving elements 3. Moreover, when a finger or an object touches a propagation path of the surface acoustic wave on the non-piezoelectric substrate 1, the surface acoustic wave is attenuated. Accordingly, it is possible to detect a touch which has been made and the touched position by finding whether the level of the receiving signals of the receiving elements 3 is attenuated. A region indicated by the broken line is a region in which the touched position can be detected (hereinafter referred to as the xe2x80x9cdetection region 1axe2x80x9d), and a peripheral region of the detection region 1a, where the excitation elements 2 and receiving elements 3 are disposed, is referred to as a xe2x80x9cframe regionxe2x80x9d.
In the touch panel device having such a structure, the resolution is determined by the aperture length of the IDT. It is therefore preferred to have a shorter aperture length. However, since there is a correlation between the aperture length and the wavelength of the surface acoustic wave, if the aperture is narrowed, the diffraction effect is suddenly enhanced and it becomes difficult to distinguish the respective tracks along which the surface acoustic waves have been propagated. Furthermore, in order to reduce the aperture, it is necessary to make the wavelength of the surface acoustic wave shorter. In this case, not only a circuit for high frequency is required because of an increase in the frequency resulting from a shorter wavelength, but also attention must be paid to the S/N ratio as the attenuation factor is increased due to scattering or the like.
Accordingly, the present inventor et al. have proposed a touch panel device (hereinafter referred to as the xe2x80x9cprior examplexe2x80x9d) in which a plurality of excitation elements and receiving elements are disposed so as to propagate the surface acoustic waves in an oblique direction (diagonal direction) of the non-piezoelectric substrate 1. FIG. 2 is an illustration showing the structure of such a touch panel device. In the structure shown in FIG. 2, a two-dimensional touched position is detected by forming the propagation paths of the surface acoustic waves between the excitation elements 2 and the receiving elements 3 so that the propagation paths are inclined at an angle of 45xc2x0 with respect to the direction of the respective sides of the non-piezoelectric substrate 1. In this example, even when the size of tracks along which the surface acoustic waves propagate is the same as that of a touch panel device having a structure as shown in FIG. 1, it is possible to improve the resolution of the position by about 1.4 times.
In the above structure, however, since a plurality of excitation elements and receiving elements are arranged into lines, if the diffraction effect is taken into consideration, a wide aperture is necessary due to this structure, and therefore there is a limit in narrowing the size of tracks along which the surface acoustic waves propagate and there is a demand for an improvement.
It is a main object of the present invention to provide a touch panel device capable of significantly improving the accuracy in detecting the position of an object (the resolution of a detected position).
A touch panel device of the first aspect of the present invention is a touch panel device comprising at least one pair of an excitation element for exciting a surface acoustic wave and a receiving element for receiving the surface acoustic wave at peripheral sections in a diagonal direction of a rectangular non-piezoelectric substrate, each of the excitation element and receiving element having an IDT constructed by joining comb-like electrode fingers to facing electrode bases, for detecting a position of an object touching the non-piezoelectric substrate by propagating surface acoustic waves between the excitation element and receiving element in the diagonal direction of the non-piezoelectric substrate and detecting the position based on reception results at the receiving element, wherein the comb-like electrode fingers of the IDTs in the excitation element and receiving element are joined to the electrode bases so that they are inclined from a facing direction of the electrode bases.
In the touch panel device of the first aspect, since the surface acoustic waves are propagated in the diagonal direction of the non-piezoelectric substrate and IDTs in which the comb-like electrode fingers are extended from the electrode bases in a direction shifted from the facing direction of the facing electrode bases are used, it is possible to continuously detect a position touched by a finger or the like, thereby enabling a significant improvement in the resolution of the detected position as compared with the prior example.
A touch panel device of the second aspect of the present invention is based on the first aspect, and the comb-like electrode fingers have an angle of inclination in two directions from the facing direction of the electrode bases. Since the surface acoustic waves in two directions are excited by a single excitation element and/or surface acoustic waves in two directions are received by a single receiving element, it is possible to efficiently perform an exciting process of the surface acoustic waves and/or a receiving process of the surface acoustic waves.
A touch panel device of the third aspect of the present invention is based on the second aspect, and the comb-like electrode fingers are bent. Since the IDTs having the comb-like electrode fingers bent in the middle are used, it is possible to excite and/or receive surface acoustic waves in two directions by a structure of one pair of electrode bases, thereby realizing a narrower frame region.
A touch panel device of the fourth aspect of the present invention is based on the second aspect, and the angle of inclination of the comb-like electrode fingers is set according to an aspect ratio of a size of an object position detection region in the non-piezoelectric substrate. Since the angle of inclination of the comb-like electrode fingers in the IDTs is set according to the aspect ratio of the detection region, it is possible to achieve a one-to-one surface acoustic wave exciting and receiving relation.
A touch panel device of the fifth aspect of the present invention is based on any one of the first through fourth aspects, and the IDTs related to surface acoustic waves propagating outside of the object position detection region are eliminated. Since the IDTs related to surface acoustic waves which do not propagate in the detection region are eliminated, it is possible to realize an efficient IDT arrangement without waste, improve the detection accuracy by eliminating the influence of noise, and reduce the frame region.
A touch panel device of the sixth aspect of the present invention is based on any one of the first through fifth aspects, and a plurality of pairs of the excitation element and receiving element are provided and a frequency of the IDTs in each pair is different from that in other pair. Since a frequency in a pair of the excitation element and receiving element is made different from a frequency in other pair of the excitation element and receiving element, it is possible to prevent a lowering of the S/N ratio due to overlapping of the surface acoustic waves.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.